Toughening up a glass jaw

It has become clear to me that, for whatever reason, I can't take much of a punch. This became very clear when I last tried my hand at MMA, and one solid overhand left punched the common sense clear out of me. I notice it in sparring as well, where there seem to be a disproportionate number of blows which buckle my knees.
So how exactly do I correct this? Strengthen neck muscles? Spar with heavy handed guys? Iron Face Qigong?

The fool thinks himself immortal,
If he hold back from battle;
But old age will grant him no truce,
Even if spears spare him.

I do have kind of a theory on this ,based on nothing more than having people hit me mind, but here we go.
To start with I think it is very simple head position the higher it is held the more likely it will move around and therefore cause concussion. From there I find pushing the top of my head toward the shot while absorbing the impact with my body worked the best for me.

The thing is, even when bettering your defense, it is almost inevitable you will be hit. Unless you outclass your opponents so much.\

That is, I'm also assuming he has been working on bettering himself in every way possible. But if there was something to help the glass jaw, why not? It's the same reason why people do a lot of cardio and conditioning. They want the best possible chance.

Certain spots on the head are simply anatomical weaknesses; specifically the temple and the chin (the "button"). Regardless of who you are, getting hit in of these spots sucks and makes you go all wobbly. How wobbly (from a bit to a complete KO), is dependent largely on your physiology, aka your genetics/body type.

Thus, for those two spots, you want to simply avoid getting hit their; learn to roll with punches, etc to mitigate the force of an impact to those spots. Learn to block properly to avoid leaving them open, etc, etc.

Now, it can also suck to get hit in the rest of the head and face. In regards to the face/nose, dealing with strikes to those areas is largely a manner of increasing pain tolerance.

In regards to the rest of the head, in these cases what is happening is your brain is rattling against your skull, which can make you wobbling/KO you. Your susceptibility to this is also genetic, but you can do a lot more to help yourself, as people have mentioned. In addition to improving your technique, neck strength helps as others have mentioned.

So one of the real questions is where are you getting hit that you are noticing a problem?

Please pardon me if this has been already asked hundreds of times, but would heavy weightlifting, headstands, and general neck strengthening (like the weight helmets in muay thai) be of any help in reducing the shock of taking a head punch?

Please pardon me if this has been already asked hundreds of times, but would heavy weightlifting, headstands, and general neck strengthening (like the weight helmets in muay thai) be of any help in reducing the shock of taking a head punch?

I don't advise weight lifting for the neck specifically, but as a general answer, yes it helps, but only for certain head punches (as I outlined in my above post). It won't help with the jaw.

One thing I'd add is that "Rolling with the punches" is not just a folksy saying. You need to learn to literally roll away from shots that you can't block or dodge. This is one thing that happened from training bare knuckle Kyokushin style sparring. Yeah it isn't the head but you learn pretty fast to twist away from shots to take the power out of them once you understand the timing you can start doing it in you kick boxing sparring too.

Two people to watch in MMA are Rampage and Fedor. Neither one of them gets caught flush very often even when shots get through. The only good way to practice this is to let people with less power land some shots on you. I'd make sure I had on head gear to start and don't tell them you are doing it.

I forgot to mention if you have any tape of you taking bad shots watch it over and over and see if something about your posture or head/shoulder positioning is letting you get hit more often. Some people that have good cover in general but still leave openings that get exposed when they throw a certain strike or combination.